The present invention relates to magnetoresistive heads and more particularly to a method and system for providing electrostatic discharge protection for magnetoresistive heads, particularly in devices using a flex-on-suspension (FOS) or trace-suspension-assembly (TSA) in a head-gimbal-assembly (HGA).
FIG. 1 is a block diagram of a portion of a suspension assembly used in magnetoresistive (MR) technology. Depicted with the suspension assembly 50 is a slider 1 including an MR head 10 used in reading magnetic recording media. Typically, the slider 1 includes a merged head. Thus, the MR head 10 is part of a merged head that also includes a write head. However, for clarity, only the MR head 10 is shown. The MR head 10 includes an MR sensor 30. Typically, the MR sensor 10 is an anisotropic magnetoresistive (MR) sensor or a giant magnetoresistive (GMR) sensor. The slider 1 also includes pads 42, 44, 46 and 48. Two pads 42 and 44 are used for making electrical contact to the MR sensor 30 from other portions of the suspension assembly 50. The other two pads 46 and 48 may be used in making electrical contact to the write head.
In order to use the MR head 10 in a disk drive, electrical connection is made to the MR sensor 30 via the pads 42 and 44. In some conventional systems, a twisted pair of wires is used to connect to the leads 42 and 44. However, the conventional suspension assembly 50 is typically provided in order to couple the MR sensor 30 to the remaining electronics (not shown).
The conventional suspension assembly 50 may include a flex-on-suspension (FOS) developed by Read-Rite Corporation of Milpitas, Calif., in a trace-suspension-assembly (TSA), in a chip on suspension (COS) or in a bridge-flex-circuit (BFC). Note that the BFC is typically coupled with the MR head 10 through the FOS, TSA or COS. Thus, as used herein a suspension assembly can refer to any combination of a FOS, a TSA, a COS, a BFC or similar structure for making electrical contact to the MR head 10. The conventional suspension assembly 50 has a wireless electrical connection with the MR head 10 that allows for a smaller form factor for the head and head-gimbal-assembly. The conventional suspension assembly 50 is typically significantly longer than the slider 1.
The conventional suspension assembly 50 is typically mechanically coupled with the slider 1 via a metal arm (not shown). The conventional suspension assembly 50 includes a first lead 52, a second lead 54, a third lead 56 and a fourth lead 58. Note, however, that the third lead 56 and fourth lead 58 may be omitted if the slider assembly 1 does not include a write head. The leads are typically surrounded by an insulating film 60. The insulating film 60 is typically made of two layers of polyimide. The film 60 generally surrounds the leads 52, 54, 56 and 58. Thus, in the conventional suspension assembly 50 the leads 52, 54, 56 and 58 are typically sandwiched between two layers of film 60. The conventional suspension assembly 50 also includes four head gimbal assembly (HGA) pads 62, 64, 66 and 68 coupled with the leads 52, 54, 56 and 58, respectively. The leads 52 and 54 are also electrically coupled with the MR sensor 30, preferably through pads 42 and 44. Thus, electrical connection can be made to the MR sensor 30 even when the MR head 10 is sufficiently small for use in present disk drives.
Although the conventional suspension assembly 50 functions, one of ordinary skill in the art will readily realize that the conventional suspension assembly 50 and head 10 are subject to electrostatic discharge (ESD) failure. During fabrication, the MR sensor 30 is often rendered inoperative. In some cases, losses may be as high as ten to twenty percent. It has been determined that these losses may be due to tribo-charging of the film 60 in the suspension assembly 50. As higher density recording media is used, the MR head 10 is built smaller to be capable of reading narrow track signals from high-density recording media. As the MR head 10 is reduced in size, more damage to the MR sensor 30 can be caused by smaller transient currents due to ESD.
For example, during manufacture, electrical contact is often made to a portion of the conventional suspension assembly 50, such as the HGA pads 62 or 64. When a charged metal fixture touches the pad 62 or 64, the charge can be transferred to the HGA pad 62 or 64. The charge on the HGA pad 62 or 64 could cause a large transient current to flow through the MR sensor 30 as the charge is discharged. Charge could be similarly transferred to the leads 52 and 54, resulting in a transient current which flows through the MR sensor 30. The transient current can easily destroy the MR sensor 30. Thus, the MR sensor 30 may be damaged or destroyed due to ESD.
Many conventional systems have been developed for protecting the MR head 10 from damage due to ESD. Some conventional methods connect a very low resistance conductor between the leads 52 and 54. The conductor typically has a resistance of only a few ohms or less. In other words, the leads 52 and 54 are shorted. As a result, the transient current can be prevented. Other conventional methods connect a very high resistance shunt between the leads 52 and 54, or between one of the leads 52 and 54 and ground. The high resistance shunt is typically on the order of 106 Ohms. The high resistance shunt allows any charge accumulated on the conventional suspension assembly 50 to be slowly dissipated. Thus, the MR sensor 30 may be preserved.
Although the very high resistance and very low resistance shunts can function, one of ordinary skill in the art will readily recognize that such shunts are typically temporary and, therefore, removable. As a result, the protection provided from ESD damage is also temporary. For example, prior to contacting a shunt with the HGA pads 62 and 64, the MR sensor 30 is not protected. Thus, the MR head 10 may still be subject to failure due to ESD induced damage during manufacture.
Accordingly, what is needed is a system and method for providing ESD protection for MR heads during fabrication. The present invention addresses such a need.
The present invention provides a method and system for providing a suspension assembly which includes a mechanism for protecting a magnetoresistive (MR) head from electrostatic discharge damage. The MR head includes an MR sensor having a first end and a second end. The method and system comprise providing a first lead and a second lead. The method and system also comprise providing an insulating film that substantially supports a first portion of the first lead and a second portion of the second lead. The MR head is coupled with the suspension assembly. The first and second ends of the MR sensor are coupled with the first and second leads, respectively. The method and system also comprise providing a conductive strip coupled with the insulating film. In one aspect, the method and system comprise providing at least one diode electrically coupling the first lead and the second lead. In another aspect, the method and system also comprise electrically coupling first lead with the conductive strip. In another aspect, the method and system also comprise electrically coupling first lead with the conductive strip and electrically coupling the first and second lead. In another aspect, the method and system comprise electrically coupling first and second leads with the conductive strip. Preferably, electric coupling is provided using at least one diode.
According to the system and method disclosed herein, the present invention provides greater robustness against damage due to electrostatic discharge.